Jane Carson, 14 year old daughter of Colonel Richard Carson, captain of the interstellar passenger ship //Urania,// leaves her home on planet Alexa to spend the summer vacation with her father. Boarding the starship on Callindra, she gets acquainted with the officers, including first navigator Major Law, an elderly gentleman; first pilot Major Wright, another elderly man whose harsh style is not to her liking; young and handsome second navigator First Lieutenant Charles; and others – and the crew, especially Cadet Platoon Four, twelve young men charmed by and making friends with her, appoint her Chief Cadet, an obsolete rank, so she is the only one in the Galaxy.

Jane, a star ship maniac with some theoretical knowledge about //Urania,// easily adapts to their military style and spends all her time with the platoon when they’re working on maintenance, or in the control room during takeoff and hyperspace jumps. She has no interest in the two thousand passengers on board.

After several hyperjumps, they are alerted to a suspicious problem in one of the numerous pieces of machinery in the engine house. Most of the officers and a platoon of cadets go there to check the error. While they are away, an emergency alarm is triggered. There is fire on board.

Following the cameras of the fire robots on screen from the controller, Jane notices something, orders Platoon Four to the control room, and orders the arrest of the rest of the officers, including Wright and Charles. Then she shows her father what she has found: the remains of a detonator.

The detonation destroys all the equipment that controls the internal airlocks, trapping most of the officers and a platoon in the engine house. They can’t come back and fly the ship which is now in the deep space of an uninhabited solar system.

Jane organizes the work, commanding the first three sectors. They work on setting the trapped people free. But after days of hard work, a cadet is injured in an accident. Jane decides to take the ship to a port immediately, no matter there is no hyperspace navigator she can trust, but she orders the arrested officers to the control room and takes the duty of the hyperspace navigation herself.

This lets her discover who caused the detonation and why, before guiding //Urania// safely to a planet.

A year later, on her next vacation on //Urania,// Jane is in the control room again when the unimaginable happens: the first case in history when two ships collide in the open deep space. The other one is //Hyperion,// a military prison ship. Both being damaged, neither one can leave the location. However, an unpleasant thought occurs to them: what if the collision caused such severe damage in the security system that the imprisoned might be set free and take over the ship? What if the crew they know are actually prisoners?

Her fears proving to be well founded, Jane takes the duty of leading armed forces and conquering the other ship, to be able to send a little space boat for help. When the help arrives, //Urania// makes a crash landing on the planet Fomina.

While //Urania// is being repaired, Jane is invited to the neighbouring planet Auwelia with her platoon, to help two hundred tourists trapped underground. Knowing nothing about the planet, they’re stunned at the sight of a grey desert with lava flows in different colors – red, orange, yellow, blue, purple – and arriving at Complex Six, they find themselves in a labyrinth of underground corridors, carved by lava in the glass-hard rock, with gemstones embedded in the walls. Jane immediately hates Auwelia, a heaven only for geologists, and wants to go home; but only when she can do so together with those waiting for rescue in an underground shelter, separated from the outside world by a lava eruption.

Jane, the platoon and the local team try everything to prevail over Auwelia, but the extremely active planet continually hinders their efforts. Finally, Jane decides there is only one solution. The lava cannot flow upwards, so they must break a hole on the bottom of the complex: they need a nuclear bomb.

After //Urania// loses half of its nuclear pile in the collision with //Hyperion,// they had to build a replacement one, and it’s now travelling to //Urania// on two tracked transport convoys, the //Saurus.// Two million tonnes each. They’re going through a grass covered plain on Fomina, when //Melissa,// a small Terraluna ship crashes into a hill after the pilot has a brain haemorrhage. He is rescued, but the wreck is blocking the way for //Saurus.// And the small ship weighs 22 thousand tonnes.

While the repairs are being carried out, they realize the danger is greater than delaying the departure of //Urania.// The damage inside //Melissa// has affected the nuclear systems, and they can calculate how much time do they have before the Fominan life is going to become endangered. They must remove the ship from that world, immediately, regardless of its inability to move.